Sound Field & Sound Phenomena

Question 1

What is the sound field?

Answer 1

The region where sound is propagated and it depends on the location within the sound field

Question 2

define sound field

Answer 2

an area where sound waves are present

Question 3

near field

Answer 3

within one wavelength of source and inverse square law doesn’t apply
ex: measuring sound in an ear canal from a HA

Question 4

far field

Answer 4

beyond the near field
includes free field and diffuse field

Question 5

free field

Answer 5

no echos
sound waves travel without obstruction
can use inverse square law if both are in here

Question 6

diffuse field

Answer 6

echoes present
incident and reflected waves
cancel each other completely out or added in regards to phase
they are being added or cancelled in this field

Question 7

In a large room with walls, with the sound source in the corner, describe near field vs. far field and describe free field vs. diffuse field. Draw and label a picture depicting these.

Answer 7

near field is one wavelength from the source
far field - beyond the near field
free field - no echos
diffuse - echos are happening

Question 8

define beats

Answer 8

two sounds close together in frequencies and there are times where each cycle it overlaps and others where it doesn’t and perceptually we hear fluctuating amplitudes

Question 9

define doppler effect

Answer 9

the sound source is moving but listener is not, pitch will change
away from listener - wavelengths get elongated and lower pitch
toward - higher pitch and wavelengths get shorter
compressions and rarefractions either get closer together or farther apart

Question 10

define sonic boom

Answer 10

when it breaks the sound barrier
moving source of sound, as it approaches, hear a pitch change and this happens when it reaches the speed of sound and goes beyond it
in front of its own sound wave compressions of the sound wave add up on one another to form a very large compression that, contains considerable sound energy
compressions on top of each other

Question 11

define standing wave

Answer 11

Wave that appears to stand still, that is the result of two sound waves in an enclosed area propagating in opposite directions

Question 12

What would happen if you were testing someone’s hearing, and you thought the amplitude of the signal was the red or blue wave, but it was really the black?

Answer 12

waveform that is twice the amp is the result of it
blue - incident
red - reflected
black - standing when they combine together

Question 13

when do standing waves occur

Answer 13

Alternation from reinforcement to cancellation
Relationship between tube length (or enclosure size) and standing wave occurring
Occurs if length of tube is ¼ of the wavelength (tube open at one end)

Question 14

What is a resonant frequency?

Answer 14

natural frequency/frequency it resonates best at

Question 15

What happens to the resonant frequency if you increase the tube length?

Answer 15

lowers

Question 16

What happens to the resonant frequency if you decrease the tube length?

Answer 16

increases

Question 17

a tube open at one end resonates at:

Answer 17

1/4 of the wavelength

Question 18

a tube open at both ends resonates at:

Answer 18

1/2 of the wavelengthW

Question 19

What is Resonant frequency of tube based on?

Answer 19

standing waves

Question 20

What are audiology applications of standing waves?

Answer 20

Calibration issues when the ear canal is involved
Hearing aid measurements
Sound field testing

Question 21

Explain the relationship between the length of an open tube (open at one end) and the resonant frequency of the tube.

Answer 21

as length gets longer, rf gets lower

Question 22

what causes standing waves?

Answer 22

when a resulting wave appears to stand still as a result from two waves in a closed area are moving in opposite directions